Treatment of steam systems



July 31, 1951 E. P. PARTRIDGE v `TREATMENT OF' STEAM SYSTEMS Filed May 30, 1945 Dumm mJm Kw4-Om M ffm ENTOR /kf ATTORNEY Patented `luly 31, 1951 TREATMENT F STEAM SYSTEMS Everett P. Partridge, Beaver, Pa., assignor to Hall Laboratories, Incorporated, Pittsburgh, Pa.

Application May 30, 1945, Serial No. 596,775

(Cl. 21o- 23) 8 Claims. 1

This invention relates to a method for preventing or retarding corrosion of steam systems by adding thereto an alkaline, water-soluble, volatile amine in accordance with the invention as hereinafter described.

The deterioration of metallic surfaces in a steam system occurs most rapidly under acid` vcarbonio acid which is formed bythe combination of water and carbon dioxide. The carbon dioxide enters the system in several different ways. Since it is a constituent of air, any air entering the system brings with it a certain amount of carbon dioxide. Carbon dioxide is dissolved in the make-up water which is added to the system. It is also a decomposition product of carbonates and bicarbonates present in the boiler Water. The Water employed in steam systems may and often does contain dissolved oxygen. When the water is heated to form steam, the dissolved oxygen is released from the water and mixes with the steam. When the steam contains a mixture of dissolved oxygen and carbon dioxide, this combination becomes extremely corrosive as the steam condenses on metal surfaces.

Generally stated, an object of this invention is to provide a method of treatment whereby the steam may be permeated with a volatilized amine to render the steam condensate materially less corrosive than it would otherwise be, and under optimum conditions to make such condensate non-corrosive.

More specifically, it is an object of this invention to provide a process whereby the condensate, in a steam system which has been treated with an effective volatile amine, may be so treated as to reconvert the spent amine into an effective form of amine salt.

Other objects of the invention and the manner of practicing the same will be apparent from the following description taken in conjunction with the table and the single figure in the drawing, in which a steam system is diagrammatically illustrated with legends to indicate the various parts thereof.

It is common practice to treat boiler water with alkaline materials such as caustic soda, and consequently there is little likelihood of acidic corrosion in the boiler. However, the alkaline alkali-metal salts and hydroxides do not, as a rule, carry overwith the steam if the boiler is operated efiiciently. Therefore, that part of the system which is in Contact with condensate from the steam does not receive the benefit of the alkaline compound which has been added to the boiler and may be exposed to acidic conditions. Corrosion, accordingly, may occur in the steam line. the condenser, and the condensate return 2 lines, unless preventive steps are taken. Dreyfus in U. S. Patent 2,053,024 discloses the use of certain water-soluble alkaline volatile amines which have been found effective in preventing or reducing acidic corrosion by steam condensate in those parts of the system which have been mentioned. In practicing this invention, the amine is dissolved in the boiler water, volatilized with the steam and condensed with the condensate so that an alkaline environment is maintained in all parts of the system. Upon leaving the boiler, the volatile amine reacts with carbon dioxide and carbonio acid to form both amine carbonates and bicarbonates, and if a slight excess of amine is added beyond that amount required to neutralize the acidic compounds, some free amine in an uncombined state will flow through the system from the boiler.

In most casessome part of the steam system between the condensate return line and the boiler is open to the atmosphere. The condensate may discharge into an open sump or hotwell, or a de-aerating or open feed-water heater may be installed for the dual purpose oi removing air from the system and heating the feedwater before it enters the boiler. Since both the amine bicarbonate and amine carbonate are fairly unstable, it is not `unusual to nd that in` passing through a hot-well or de-aerating heater they are decomposed into free amine and free carbon dioxide. A considerable portion of any uncombined amine may thereby escape from the system through such an opening under these conditions. Although it is extremely desirable to remove as much carbon dioxide from the system as possible, the loss of volatile amine is undesirable, as it should be retained for re-combination with additional carbon dioxide subsequently brought into the system.

In accordance with my invention, the amine introduced into the system to prevent or retard acidic corrosion is conserved by regenerating it or rendering it available for protecting the system over and over again thereby conserving expensive chemicals. I have found that the addition of certain water-soluble acid-reacting compounds to the condensate return water will not only materially reduce the loss of free amine from the system but Will also assist in the liberation of carbon dioxide. I may make this addition at any convenient point between the condensate return line and the boiler. Where a de-aerating heater is installed ahead of the boiler, the addition should be made to the water as it enters the heater or at some convenientpoint in the condensate return line preceding the heater. In order to expose as little as possible of the condensate return line to water at a llowered pH value, it is desirable that the acid-reacting compound be added to the water close to or at the 3 point of entry into the heater, or should be introduced separately into the heater. If a heater is not installed, the addition can be conveniently made at the sump or hot-well into which the condensate return water is discharged.

In the table, I enumerate the various stages through which a volatile amine passes in a steam system, to which I have added certain acid-forming compounds.

TABLE 1. Boiler Water is vaporized to produce steam.

Bicarbonates and carbonates are hydrolyzed liberating carbon dioxide which passes off in steam, leaving residual alkalinity in boiler water.

Dissolved amine is volatilized, mixing with steam.

2. Steam line Steam containing admixed carbon dioxide and amine passes to condensing unit.

3. Condens-ing unit Steam condenses to Water.

Carbon dioxide and amine dissolve in water, amine neutralizing to the desired degree the acidity produced by carbon dioxide.

4. Acid treating at hot-well, sump, feed water heater or other suitable place Acid xes amine as non-volatile dissolved salt,

liberates carbon dioxide which escapes to atmosphere.

5. Boiler Amine is regenerated by action of alkalinity of boiler water on amine salt, leaving alkali-metal salt in solution in boiler water.

Regenerated amine passes out with steam.

In the table, I have shown the addition of sulfuric acid, as a typical acid-reacting compound, to the condensate return water at the hot-well or some other suitable place. In treating boiler waters to reduce acidic corrosion with a volatile alkaline amine, it is generally the practice to add suflicient amine to raise the pH value of the condensate Water to about 8.3. Additional amine may be added but it is unnecessary to maintain the condensate water at high pH values. Thedesired point can be readily determined by the use ofphenolphthalein or some other suitable indicator which is added to samples of condensate. The addition of a very small quantity of sulfuric acid to the condensate return water will cause the evolution of carbon dioxide and the concurrent formation of an amine sulfate as shown in stage 4 -of the table. In practice, suilicient acidv is added to combine completely with the amine bicarbonate, amine carbonate, and free amine which is present in the condensate (stage 3). To assure a minimum loss of volatile amine, an excess of acid should be added, although the Water in the feedwater heater and the line running to the boiler should not have too low a pH value if this equipment is subject to acid corrosion` The pH of the feedwater effluent after carbon dioxide has been lost in the heater, hot-well, or sump should be somewhat below 7, a value of 5.5 being satisfactory. The pH value of the feedwater ellluent need be no lower than that corresponding to the color change of methyl orange, which is about 4.0, in order to insure good retention of amine and good ample, if a pH value of about 4.0 is to be main-- tained, I may use methyl orange. If a pH value of about 5.0 were desired, methyl red might be used. I may also use a mixed indicator which responds to changes of pH value by exhibiting color changes over an extensive range.

In those steam systems Which do not employ a feedwater heater, the amine salt may be formed in the hot-well or sump by adding the acidreacting compound. The amine salts of any of the acid-reacting compounds which I use for accomplishing the desired results are quite stable at temperatures even above the boiling point of water under atmospheric pressure, so that even though the condensate return Water may be heated to a temperature of 200-212 F., only a trace of free amine will be lost from the system.

As indicated in stage 5 of the table, the stable amine salt of the acid-reacting compound used in my treatment enters the boiler and upon reaction With the caustic soda present in the boiler, a Water-soluble alkali-metal salt and free amine are formed. Thus the alkali-metal salt remains in the boiler and the amine is volatilized and proceeds through the system with the steam to recombine with additional carbon dioxide and carbonic acid which may have been brought into the system.

In practicing my invention, I may employ any acid-reacting compound which will react with the amine carbonates, amine bicarbonates, and free amines in the condensate return Water to form amine salts and carbon dioxide or carbonio acid. Among the inorganic acids which would be eiective are sulfuric, sulfurous, nitric, phosphoric, phosphorous, pyrophosphoric, hydrochloric, and hydroluoric acids. Any organic acid capable of liberating CO2 from the condensate return water may be used. Acetic acid, formic acid, and propionic acid would be suitable. Generally speaking, any Water-soluble acid having a dissociation product greater than that of carbonic acid would react to liberate carbon dioxide and form an amine salt. The dissociation prodevolution of carbon dioxide. However, if aciduct of carbonio acid measured at a temperature of 18 C. is 3.5 10-7.

I have also found that certain acid-reacting salts will cause the evolution of carbon dioxide from the condensate return Water and will unite with the amines to form amine salts. Alkalimetal acid-reacting salts, such as acid orthophosphates, pyrophosphates, tripolyphosphates, alkali-metal phosphate glasses with molar ratios of alkali-metal oxide to P205 of less than l, sulfates, sultes, uorides, acetates, hypophosphites, hypophosphates, phosphites, oxalates, pyrosulfates, pyrosulftes, and tartrates capable of evolving carbon dioxide from the condensate return water under the conditions therein present, can be successfully employed in practicing my invention. I

Certain acid-reacting compounds in the gaseous state may be used. Sulfur dioxide, for

example, could be introduced into the condensate return thereby forming an amine sulte and releasing carbon dioxide. The cost of the acidreacting material and ease of handling it under the circumstances surrounding its use would largely govern the choice of a speciiic material.

Although the use of an acid-reacting cornpound will materially reduce the loss of lamine through volatilization, it may be necessary to add small quantities of fresh amine to the steam system from time to time. These additions, however, will be negligible as compared with the amount of fresh arne required where acid-reacting compounds a. tot employed. Whether fresh amine is required can be readily determined through an examination of the pH value of the condensate. For example, Where it isdesired to maintain the condensate at a pH value corresponding to the color` change of phenolphthalein,

if a pink color is observed when phenolphthalein indicator is added to a sample of this water, following the application of my method of treatment, added amine may not be necessary and further addition may be deferred until the pH value of the condensate water is such that the indicator solution produces no color when added to the sample of condensate.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

l. The method of reducing the loss of alkaline water-soluble volatile amines from the return condensate water of steam systems to which an alkaline water soluble volatile amine has been added, which consists essentially of maintaining a strong base substance in the evaporating zone of the system, adding to the return condensate water at any suitable point between the condensing zone and the evaporating zone of the system, a water-soluble acid-reacting compound having a dissociation product greater than that of carbonio acid, thereby releasing carbon dioxide and minimizing the loss of amine, whereupon an amine salt of said acid-reacting compound is formed, and passing said amine salt into the evaporating zone of the system.

2. 'I'he method as described in claim 1 wherein the amount of acid-reacting compound is at least suicient to completely neutralize the methyl orange alkalinity of the condensate return water When measured after release of carbon dioxide.

3. The method as described in claim 1 wherein the amount of acid-reacting compound is sufiicient to produce a pH value of the condensate return water which is in the range of from about 4.0 to about 5.5 when measured after release oi carbon dioxide.

4. The method as described in claim 1 in which the water-soluble acid-reacting compound is one containing the NO3 radical.

5. The method of reducing the lo'ss of alkaline water-soluble volatile amines from'the return condensate water of steam systems to which an alkaline water-soluble volatile amine has been added, which consists essentially of maintaining a strong base substance in the evaporating zone of the system, adding to the return condensate water at any suitable point between the condensing zone and the evaporating zone of the system, a water-soluble inorganic acid having a dissociation product greater than that of carbonio acid, thereby releasing carbon dioxide and minimizing the loss of amine, whereupon an amine salt ofthe inorganic acid is formed, and passing said amine salt into the evaporating zone of the system.

6. The method of reducing the loss of alkaline water-soluble Volatile amines from the return condensate Water of steam systems to which an alkaline water soluble volatile amine has been added, which consists essentially of maintaining a strong base substance in the evaporating zone of the system, a water-soluble organic acid hav` ing a dissociation product greater than that of carbonio acid, thereby releasing carbon dioxide and minimizing the loss of amine, whereupon an amine salt of the organic acid is formed, and passing said amine salt into the evaporating zone of the system.

7. The method of reducing the loss of alkaline water-soluble volatile amines from the return condensate water of steam systems to which an alkaline water soluble volatile amine has been added, which consists essentially of maintaining a strong base substance in the evaporating zone of the system, adding to the return condensate water at any suitable point between the condensing zone and the evaporating zone of the system, a water-soluble acid-reacting salt of an inorganic acid, said salt having a dissociation product greater than that of carbonio acid, thereby releasing carbon dioxide and minimizing the loss of amine, whereupon an amine salt of the inorganic acid is formed, and passing said amine salt into the evaporating zone of the system.

8. 'I'he method of reducing the loss of alkaline water-soluble Volatile amines from the return condensate water of steam systems to which an alkaline water soluble volatile amine has been added, which consists essentially of maintaining a strong base substance in the evaporating zone of the system, adding to the return condensate water at any-suitable point between the condensing zone and the evaporating zone of the system, a water-soluble acid-reacting salt of an prganic acid, said salt having a dissociation product greater than that of carbonio acid, thereby releasing carbon dioxide and minimizing the loss of amine, whereupon an amine salt of the organic acid is formed, and passing said amine salt into the evaporating zone of the system.

EVERE'IT P. PARTRIDGE,

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 848,733 Fitts Apr. 2, 1907 1,395,730 Reichinstein Nov. 1, 1921 1,693,065 White Nov. 27, 1928 1,759,615 Hall May 20, 1930 1,841,825 Kriegsheim Jan. 19, 1932 1,903,041 Hall et al. Mar. 28, 1933 1,910,979 Applebaum May 23, 1933 2,046,308 Rice June 30, 1936 2,053,024 Dreyfus Sept. 1, 1936 2,074,380 Flett Mar. 23, 1937 2,196,261 Howland et al Apr. 9, 1940 2,247,711 Ralston July 1, 1941 2,304,805 Denham Dec. 15, 1942 21,328,551 Gunderson Sept. '7, 1943 2,370,473 King Feb. 27, 1945 

